This grant seeks to determine the mechanism by which short-chain fatty acids (SCFAs) regulate Na efflux by the Na/K ATPase at the basolateral membrane of colonocytes. SCFAs are a major non-endocrine stimulator of transcellular Na absorption by the colon. There is evidence in the literature to suggest that increasing luminal SCFAs may be an effective combatant of diarrheal secretion and an effective therapy for inflammatory bowel disease. Work performed by the applicant (the subject of the current R01) demonstrated that stimulation of transcellular Na absorption by SCFAs involves activation of apical Na/H exchange. Transcellular Na transport requires a concomitant increase in Na efflux at the basolateral membrane presumably via a stimulation of the Na/K ATPase. The focus of this FIRCA grant is to confirm this putative increase in Na/K ATPase activity and to determine the mechanism by which its activity is increased by SCFAs. Preliminary data by the foreign PI indicates a persistent increase in Na/K ATPase activity following a 20 min exposure of cultured colonocytes (HT29-C1) cells to SCFAs. The foreign PI will further evaluate factors involved in this effect and determine if it results from a change in intracellular Na or pH (related to a stimulation of Na/H exchange) or from changes in the intracellular level second messengers such as cAMP or Ca2+. In addition, studies are proposed to evaluate possible interactions between regulation of Na/K ATPase by SCFAs and receptor antagonists of cAMP and calcium.